A semiconductor manufacturing system, such as that shown in FIG. 1, uses an ion implanter to implant a semiconductor wafer with ions. The ion implanter includes a process chamber which is coupled to a shaft; the shaft causes the process chamber to move along an axis to implant the wafers. The process chamber changes direction at both ends of the shaft. The shaft, which functions as a chamber drivescrew, is rotated using a drivescrew motor. The motor, and thus the movement of the process chamber shaft, is controlled by a dose controller which provides motor drive pulses to the motor via a translator circuit. If the process chamber ceases movement at a location other than either end of the axis and the beam is not intercepted, striping of the wafer may occur. Accordingly, it is desirable to provide a monitoring device to determine whether the process chamber is moving along the axis.
Such a monitor device prevents striping of production wafers by detecting when the process chamber is not moving. For example, a Y-scan monitor device, available from Sumomoto Eaton Inc. located in Tokyo, Japan, monitors the motion of a Y-scan process chamber by attaching an encoder to the shaft of the semiconductor manufacturing device. As the shaft rotates, the encoder sends clock pulses to the monitor device to indicate that the processor chamber is moving up and down. If the shaft stops rotating, the monitor device activates an alarm to indicate a malfunction. Additionally, the monitor device sends a hold signal to the dose controller, which sends a flag control signal to the endstation controller. The endstation controller sends a control signal to a solenoid, which is located within a pneumatic box. The pneumatic box houses solenoids, relays, and valves that operate various assemblies on the endstation of the implanter. An example of such a pneumatic box is manufactured by EATON Corp. as part of the Ion Implanter available under the trade designation NOVA 10-80 Ion Implanter. The solenoid causes a flag to actuate, thus interrupting the flow of ions from the process chamber to the wafer.
The monitor device is clocked by the motor drive pulses which are generated by the dose controller. Accordingly, when the motor drive pulses are not provided to the monitor circuit, the monitor device cannot detect malfunctions of the semiconductor system. If the motor stops and the monitor circuit does not detect a malfunction, then the ion beam burns a stripe onto the wafers that are being implanted. Additionally, because the monitor circuit controls the flag controller, if the monitor circuit malfunctions, the flag controller does not cause the flag to actuate. Accordingly, it is desirable to provide a monitor circuit which detects malfunctions of the process chamber which may be related to the motor drive pulses.